Method, control appliance, and computer program for detecting defective pressure sensors in an internal combustion engine

ABSTRACT

A method, a control unit, and a computer program for detecting a defective intake-manifold pressure sensor and/or a defective ambient-pressure sensor in an internal combustion engine having a variable valve timing are provided. The desired detection is carried out exclusively on the basis of a direct evaluation of the pressure upstream from the throttle valve and the pressure in the intake manifold. This method eliminates the need for deriving load signals from these pressures, at least for the determination as to whether at least one of the pressure sensors is defective.

FIELD OF THE INVENTION

The present invention relates to a method, a control unit, and acomputer program for detecting a defective intake-manifold pressuresensor and/or a defective ambient-pressure sensor in an internalcombustion engine.

BACKGROUND INFORMATION

An intake-manifold pressure sensor is used, for example, to diagnose theexhaust-gas recirculation in an internal combustion engine and thereforesupplies important information for a control unit to control theinternal combustion engine. A load signal representing the current loadof the internal combustion engine, or the setting of a correct torqueselected by the driver, may be derived from the pressure in the intakemanifold. In addition, an optimum injection time in an internalcombustion engine having throttle control may be ascertained from theload signal.

Because of the high importance of the intake-manifold pressure sensorduring the operation of an internal combustion engine, it is desirablefor defects in the intake-manifold pressure sensor to be diagnosedearly.

Diagnostic methods for detecting the defectiveness of intake-manifoldpressure sensors are known in the related art, but only in the case ofconventional gasoline engines, in particular spark-ignition engines. Theconventional internal combustion engines are distinguished in that theirload control is implemented via the throttle valve, where there is afixed relationship between the pressure in the intake manifold and theload, or between the throttle-valve angle and the load.

An example of such a diagnostic method for conventional spark-ignitionengines is described, e.g., in published German patent document DE 19946 874. Here, three different signals L1, L2, and L3 are produced fromdifferent operating parameters, L1 representing the mass flow rate ofair that flows into an intake manifold of the spark-ignition engine, L2representing the pressure in the intake manifold, and L3 representing afuel signal ascertained from the mass flow rate of fuel. These signalsare compared to each other in pairs and united to form combinations whenvariations occur. Different combinations of deviations are assigneddifferent causes, i.e., different sources of error, for the deviations.Thus, e.g., in a first part of the method, it can initially be deducedthat, when a particular deviation is present, either the intake-manifoldpressure sensor and/or the exhaust-gas recirculation valve is defective.In a further part of the method, it may then be determined moreaccurately if the intake-manifold pressure sensor or the exhaust valveis defective. To this end, the pressure in the intake manifold duringboth the operation of the engine and its stoppage is measured andevaluated during the post-operation of the corresponding engine controlunit. If the intake-manifold pressure is the same in both cases, it maybe deduced that there is a defect in the intake-manifold pressuresensor; however, if the pressure in the intake manifold while the engineis stopped is less than that when the engine is being operated, it maythen be deduced that an exhaust-gas recirculation valve is defective.

In addition, ambient-pressure sensors for use in internal combustionengines are known in the related art. In addition to the intake-manifoldpressure sensors, they also supply important information for a controlunit to control an internal combustion engine. Ambient-pressure sensorsare used for, inter alia, ascertaining the maximum torque of theinternal combustion engine. Diagnostic methods for ambient-pressuresensors are also known in the art. In conventional gasoline engines inwhich the load is controlled via the throttle valve, an ambient-pressuresensor can, however, only be checked for its correct method offunctioning, i.e., plausibility-checked, while starting or during fullload, since in conventional gasoline engines, a pressure that approachesambient pressure is only present in the intake manifold under theseconditions.

However, in internal combustion engines having variable valve timing,i.e., in internal combustion engines having throttleless load control,the load of the internal combustion engine is no longer controlled viathe throttle valve and, therefore, via the pressure in the intakemanifold, but rather via a change in its valve timing and/or its valvelift. The internal combustion engines having fully variable valve timingare distinguished by a lower fuel consumption than conventional gasolineengines.

FIG. 3 schematically illustrates such an internal combustion engine 100having variable valve timing. Internal combustion engine 100 includes anengine block 110 having a piston 112, which moves up and down in it.Connected to the engine block is an intake manifold 120 having abuilt-in throttle valve 122 and an exhaust pipe 130. However, incontrast to conventional spark-ignition engines, throttle valve 122 isnot used for controlling load. The control of the air supply and airexhaust through the intake manifold and the exhaust pipe, and thereforethe control of the load of the internal combustion engine, is carriedout via valves 140, which are controlled by a control unit 200, thecontrol being implemented with the aid of fully variable timing edges.Instead of a single control unit 200, several control unitsinterconnected by any communication link may also be used forcontrolling valves 140. The valves may be moved, for example, byelectromagnetic or electrohydraulic actuators.

Control unit 200 includes an ambient-pressure sensor 210 for supplying athrottle-valve pressure signal, which represents pressure p_before_DKupstream from throttle valve 122. In this context, ambient-pressuresensor 210 does not directly supply pressure p_before_DK, but itprimarily supplies only the ambient pressure, i.e., the air pressureupstream from air filter 150 of the internal combustion engine. Then,actual pressure p_before_DK upstream from the throttle valve may besubsequently derived in either ambient-pressure sensor 210 itself orcontrol unit 200, by subtracting a pressure drop occurring in air filter150 of the internal combustion engine from the measured ambientpressure.

In throttleless operation of the internal combustion engine, thepressure upstream from the throttle valve must be equal to the pressurein the intake manifold. An intake-manifold pressure sensor 220 istypically provided in the case of the control units of the related art.Intake-manifold pressure sensor 220 provides an intake-manifold pressuresignal, which represents pressure p_intake in intake manifold 120 ofinternal combustion engine 100. Sometimes, they are additionallyprovided with an ambient-pressure sensor 210.

However, as explained above, since the load control in internalcombustion engines having fully variable valve timing is no longerimplemented via the throttle valve, all of the already known diagnosticmethods for pressure sensors, which are based on deriving a load signalrepresenting the load of the internal combustion engine from the angularposition of the throttle valve or the pressure in the intake manifold,are no longer applicable to internal combustion engines having fullyvariable valve timing.

Therefore, an object of the present invention is to provide a method, acontrol unit, and a computer program for detecting a defectiveintake-manifold pressure sensor and/or a defective ambient-pressuresensor in internal combustion engines having fully variable valvetiming.

SUMMARY

This object is achieved by the method, control unit, and programaccording to the present invention. In contrast to the related art, thepresent method dispenses with deriving load signals from the position ofthe throttle valve or from the intake-manifold pressure for detecting ifat least one of two pressure sensors, namely the intake-manifoldpressure sensor or the ambient-pressure sensor, is defective. Instead,the method of the present invention allows this detection to take placeexclusively on the basis of a direct evaluation of the pressure upstreamfrom the throttle valve and the pressure in the intake manifold.

According to an example embodiment, the method includes further steps,in order to be able to determine which of the two pressure sensors isdefective. To this end, the internal combustion engine havingthrottleless load control is artificially shifted into an operatingstate, which simulates throttled load control. In the scope of thissimulation, it is also possible to then derive simulated load signalsfrom both the pressure in the intake manifold and the angular positionof the throttle valve. According to the present invention, the simulatedload signals are used for identifying the pressure sensor that isactually defective.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a shows an example embodiment of a method of the presentinvention for detecting defective pressure sensors in an internalcombustion engine and a first logic module provided for implementing themethod.

FIG. 1 b shows an example embodiment of a control unit of the presentinvention.

FIG. 2 shows another example embodiment of the method according to thepresent invention and a second logic module provided for implementingthe further refinement.

FIG. 3 shows a conventional internal combustion engine having variablevalve timing, and a corresponding, conventional control unit forcontrolling the valves.

DETAILED DESCRIPTION

FIG. 1 a illustrates a method for determining whether or not at leastone of two pressure sensors, namely the intake-manifold pressure sensorand/or the ambient-pressure sensor, is defective in the case of aninternal combustion engine having variable valve timing as shown in FIG.3. The method steps illustrates FIG. 1 a do not allow one tospecifically determine which of the two pressure sensors is defective;such a determination may be made with the aid of further steps of themethod described below with reference to FIG. 2.

The method is illustrated in FIG. 1 a by showing the functional layoutof a first logic module 240 according to the present invention, whichmay be a component of a control unit 200 for controlling the valves ofinternal combustion engine 100, which control unit 200 is shown in FIG.1 b. First logic module 240 allows the claimed method to be implemented.The layout of first logic module 240 is described below in detail; theindividual steps of the claimed method may also be deduced from this.

According to FIG. 1 a, first logic module 240 receives both athrottle-valve pressure signal, which represents pressure p_before_DK,and an intake-manifold pressure signal, which represents pressurep_intake in the intake manifold of the internal combustion engine.Generation of these signals is described below in connection with FIG.3. According to the present invention, first logic module 240 alsoreceives a first status signal from a first operating-state detector230, the first status signal indicating whether or not the internalcombustion engine is being operated in a throttleless operating state.As an alternative, the status signal may also be generated by anotherlogic module inside control unit 200.

As shown in FIG. 1 a, logic module 240 includes a first subtraction unit242 for calculating a pressure difference delta_p by subtraction of theintake-manifold pressure signal from the throttle-valve pressure signal.This pressure difference is supplied to a first comparator unit 244,which determines if pressure difference delta_p is greater than a firstthreshold value Delta_P1. A first AND gate 246 ANDs the logical outputsignal of first comparator unit 244 and the first status signal. Theoutput signal of this first AND gate 246 makes a first statement as towhether or not one of pressure sensors 210, 220 is defective; this isexactly the case, when pressure difference delta_p is actually greaterthan first threshold value Delta_P1 and internal combustion engine 100is simultaneously being operated in a throttleless manner, as indicatedby the first status signal. In this context, first threshold valueDelta_P1 may be set to approximately zero.

Irrespective of this first statement, first logic module 240 includes asecond comparator unit 248 for determining if pressure differencedelta_p is less than second threshold value Delta_P2, where Delta_P2 maybe zero. When this is the case, then, independently of the firststatement, it is possible to make a second statement that one of the twopressure sensors 210, 220 is operating incorrectly. This statement isphysically based on the fact that the pressure in intake manifold 120can never be greater than the pressure upstream from throttle valve 122.

First logic module 240 also includes an OR gate 249 for ORing the outputsignal of first AND gate 246 and the output signal of second comparatorunit 248. This OR operation is used for generating a first error signalE_DS_DSU, which represents an error in one of the two pressure sensors210, 220, when such an error has already been detected at either theoutput of first AND gate 246 or at the output of second comparator unit248 or at both outputs.

FIG. 2 illustrates another example embodiment, which is a furtherrefinement of the method represented in FIG. 1, this further refinementbeing used to allow an exact determination as to whether theintake-manifold pressure sensor or ambient-pressure sensor 210 isdefective. This further refinement is implemented in the form of asecond logic module 250, which may be assigned to control unit 200 aswell, as shown in FIG. 1 b.

According to FIGS. 1 b and 2, second logic module 250 implements theabove-mentioned further refinement of the method by logically combiningfirst error signal ES_DS_DSU, a first load signalload_from_intake-manifold-pressure, which represents the load of theinternal combustion engine derived from the pressure in the intakemanifold, and a second load signal load_from_DK, which represents theload of the internal combustion engine derived from the angular positionof throttle valve 122.

To implement the further refinement of the method, an operating statethat includes throttled load control is simulated in the internalcombustion engine 100 having absolutely variable valve timing. To thisend, valves 140 are controlled by control unit 200, using fixed timingedges. This special operating state is represented by a second statussignal B_DK_occurred, which is likewise supplied to second logic module250 as an input variable.

Second logic module 250 includes a second subtraction unit 251 forcalculating a load difference by subtraction of the second load signalfrom the first load signal, as shown in FIG. 2. An absolute-valuegenerator 252 calculates the absolute value of the load differencebefore this is supplied to a third comparator unit 253. Third comparatorunit 253 determines if the absolute value of the load difference isgreater than a third threshold value Delta_load.

A second AND gate 254 ANDs first error signal E_DS_DSU and second statussignal B_DK_occurred. The output signal of second AND gate 254 istransmitted, together with the output signal of third comparator unit253, to a third AND gate 255, which means that the output signal ofthird AND gate 255 represents the result of ANDing the mentioned,inputted signals. In other words: the output signal of third AND gate255 represents a second error signal E_DS_intake, i.e., it indicates, ifapplicable, the defectiveness of intake-manifold pressure sensor 220.Such defectiveness is present, when the absolute value of the differenceof the load of the internal combustion engine derived from the pressurein the intake manifold and the load derived from the angle of thethrottle valve is greater than third threshold value delta_load, andwhen, in addition, the presence of a defect in at least one of thepressure sensors, ambient-pressure sensor 210 or intake-manifoldpressure sensor 220, was simultaneously detected in the preliminaryprocedure described above with reference to FIG. 1 a, and when anoperation that includes throttled load control was simulated in internalcombustion engine 100. The conclusion that the intake-manifold pressuresensor is defective is valid, since signal load_from_DK is reliablymonitored by other diagnoses and is therefore correct.

Second logic module 250 further includes a fourth AND gate 256 forANDing the output signal of comparator unit 253 inverted by an inverter257 and the output signal of second AND gate 254, as shown in FIG. 2.The output signal of fourth AND gate 256 represents a third error signalE_DS_Umg, which indicates, if applicable, a defect in ambient-pressuresensor 210. Such a defect is present when the absolute value of thedifference of the load of the internal combustion engine derived fromthe pressure in the intake manifold and the load derived from theangular position of the throttle valve is less than or equal to thirdthreshold value Delta_load, and, at the same time, a defect in at leastone of pressure sensors 210, 220 was already absolutely detected in thepreliminary procedure described above with reference to FIG. 1, and anoperation that includes throttled load control was simulated in theinternal combustion engine.

Both the first and second logic modules may each be implementedindependently of each other in the form of a hardware circuit.

The method of the present invention, and therefore also the first and/orsecond logic module 240, 250, may be implemented in the form of acomputer program. In this context, the computer program is executable ona computing element, e.g., on a microprocessor in control unit 200, andis suitable for carrying out the method of the present invention. Inthis case, the present invention is therefore implemented by thecomputer program. The computer program may be stored in a memoryelement. In particular, an electrical storage medium, e.g., arandom-access memory (RAM), a read-only memory (ROM), or a flash memory,may be used as the memory element.

1. A method for detecting a defect in at least one of an intake-manifoldpressure sensor and an ambient-pressure sensor in an internal combustionengine having a variable valve timing, comprising: ascertaining apressure upstream from a throttle valve of the internal combustionengine; ascertaining a pressure in an intake manifold of the internalcombustion engine; calculating a pressure difference by subtracting thepressure in the intake manifold from the pressure upstream from thethrottle valve; comparing the pressure difference to at least one of: a)a first threshold value during throttleless operation of the internalcombustion engine; and b) a second threshold value during one ofthrottled and unthrottled operation of the internal combustion engine;and determining that at least one of the intake-manifold pressure sensorand the ambient-pressure sensor is defective, if at least one of: a) thepressure difference is greater than the first threshold value; and b)the pressure difference is less than the second threshold value.
 2. Themethod as recited in claim 1, wherein at least one of the firstthreshold value and the second threshold value is set to a value ofapproximately zero.
 3. The method as recited in claim 1, wherein afterdetermining that at least one of the intake-manifold pressure sensor andthe ambient-pressure sensor is defective, the method further comprising:adjusting the internal combustion engine to an operating state thatsimulates an operation having fixed timing and throttled load control;ascertaining a first load of the internal combustion engine from thepressure in the intake manifold; ascertaining a second load of theinternal combustion engine from an angular position of the throttlevalve; calculating a load difference by subtracting the second load fromthe first load; comparing an absolute value of the load difference to athird threshold value; and determining that the intake-manifold pressuresensor is defective, if the absolute value of the load difference isgreater than the third threshold value, and determining that theambient-pressure sensor is defective, if the absolute value of the loaddifference is one of less than and equal to the third threshold value.4. The method as recited in claim 3, wherein the third threshold valueis set to a value of approximately zero.
 5. The method as recited inclaim 1, wherein after determining that at least one of theintake-manifold pressure sensor and the ambient-pressure sensor isdefective, the method further comprising: adjusting the internalcombustion engine to an operating state that simulates an operationhaving fixed timing and throttled load control; ascertaining a firstload of the internal combustion engine from the pressure in the intakemanifold; ascertaining a second load of the internal combustion enginefrom a measuring signal of a hot-film air-mass flow-rate sensor;calculating a load difference by subtracting the second load from thefirst load; comparing an absolute value of the load difference to athird threshold value; and determining that the intake-manifold pressuresensor is defective, if the absolute value of the load difference isgreater than the third threshold value, and determining that theambient-pressure sensor is defective, if the absolute value of the loaddifference is one of less than and equal to the third threshold value.6. A control unit for controlling an internal combustion engine having avariable valve timing, comprising: an intake-manifold pressure sensorfor providing an intake-manifold pressure signal that represents thepressure in an intake manifold of the internal combustion engine; anambient-pressure sensor for providing a throttle-valve pressure signalthat represents the pressure upstream from a throttle valve; a firstoperating state detector for providing a first status signal thatrepresents a throttleless operating state of the internal combustionengine; and a first logic module for determining whether at least one ofthe intake-manifold pressure sensor and the ambient-pressure sensor isdefective, by logically combining the intake-manifold pressure signal,the throttle-valve pressure signal, and the first status signal.
 7. Thecontrol unit as recited in claim 6, wherein the first logic modulecomprises: a subtraction unit for calculating a pressure difference bysubtracting the intake-manifold pressure signal from the throttle-valvepressure signal; a first comparator unit for determining whether thepressure difference is greater than a first threshold value; a secondcomparator unit for determining whether the pressure difference is lessthan a second threshold value; and a first AND gate for ANDing a logicaloutput signal of the first comparator unit and the first status signal.8. The control unit as recited in claim 7, wherein the first logicmodule further comprises an OR gate for outputting a first error signalthat represents a defect in at least one of the intake-manifold pressuresensor and the ambient-pressure sensor, the OR gate generating the firsterror signal by ORing an output signal of the first AND gate and anoutput signal of the second comparator unit.
 9. The control unit asrecited in claim 7, wherein the first logic module is configured as ahardware circuit.
 10. The control unit as recited in claim 8, furthercomprising: a second logic module for determining whether at least oneof the intake-manifold pressure sensor and the ambient-pressure sensoris defective, by logically combining the first error signal, a secondstatus signal that indicates whether the internal combustion engine isset to an operating state having fixed timing edges and throttled loadcontrol, a first load signal that represents a load of the internalcombustion engine derived from the pressure in the intake manifold, anda second load signal that represents a load of the internal combustionengine derived from an angular position of the throttle valve.
 11. Thecontrol unit as recited in claim 10, wherein the second logic modulecomprises: a second subtraction unit for calculating a load differenceby subtracting the second load signal from the first load signal; anabsolute-value generator for calculating an absolute value of the loaddifference; a third comparator unit for determining whether the absolutevalue of the load difference is greater than a third threshold value; asecond AND gate for ANDing the first error signal and the second statussignal; a third AND gate for generating a second error signal thatrepresents a defect in the intake-manifold pressure sensor, by ANDing anoutput signal of the third comparator unit and an output signal of thesecond AND gate; an inverter for inverting the output signal of thethird comparator unit; and a fourth AND gate for generating a thirderror signal that represents a defect in the ambient-pressure sensor, byANDing the inverted output signal of the third comparator unit and theoutput signal of the second AND gate.
 12. The control unit as recited inclaim 11, wherein the second logic module is configured as a hardwarecircuit.
 13. A computer-readable storage medium for storing a pluralityof computer-executable instructions to be executed on a computingelement of a control unit for controlling an internal combustion enginehaving a variable valve timing, wherein the instructions, when executedon the computing element, control a method for detecting a defect in atleast one of an intake-manifold pressure sensor and an ambient-pressuresensor in an internal combustion engine having a variable valve timing,the method comprising: ascertaining a pressure upstream from a throttlevalve of the internal combustion engine; ascertaining a pressure in anintake manifold of the internal combustion engine; calculating apressure difference by subtracting the pressure in the intake manifoldfrom the pressure upstream from the throttle valve; comparing thepressure difference to at least one of: a) a first threshold valueduring throttleless operation of the internal combustion engine; and b)a second threshold value during one of throttled and unthrottledoperation of the internal combustion engine; and determining that atleast one of the intake-manifold pressure sensor and theambient-pressure sensor is defective, if at least one of: a) thepressure difference is greater than the first threshold value; and b)the pressure difference is less than the second threshold value.
 14. Thecomputer-readable medium as recited in claim 13, wherein thecomputer-readable storage medium is one of a diskette, a compact disk,and an EPROM.